The invention pertains to methods of forming photoresist on semiconductor wafers, as well as to reticle forming methods.
Photolithography is frequently utilized in modern semiconductor component fabrication. In photolithography, a reticle is formed and utilized to pattern light. The patterned light is impacted on photoresist to selectively expose some portions of the resist to the light, while leaving other portions not exposed. The photoresist is then exposed to a solvent which selectively removes either the exposed or unexposed portions to accordingly pattern the layer of photoresist.
Difficulties in semiconductor wafer fabrication can occur in forming a reticle. Reticles are typically formed by providing a layer of photoresist over a quartz substrate, and subsequently exposing portions of the photoresist to a beam of radiation while leaving other portions not exposed. The beam of radiation can be, for example, either a laser beam or an electron beam. The beam is moved slowly across an entirety of a surface of the photoresist to pattern the photoresist. Such process can take about eight hours for a laser etch, or about 24 hours for an electron beam etch. Electron beam etching is generally more precise than laser etching. However, due to the long exposure time of electron beam etching, it is often found that regions of the wafer which were initially exposed to an electron beam will process differently than portions exposed later through the electron beam. Accordingly, laser beam etching will cause non-uniformity across a reticle surface. Even with the relatively short exposure times of a laser etch, there can be non-uniformity across a reticle surface. However, such non-uniformity is generally less than that which occurs with electron beam etching.
After the photoresist is exposed to either the laser etch or the electron beam etch, it is subjected to a solvent which selectively removes either the portion of the photoresist exposed to the radiation, or the portion not exposed, to pattern the photoresist. The patterned photoresist is then subsequently used as a mask during an etch of the underlying reticle substrate, to ultimately form a patterned reticle from the substrate.
It would be desirable to develop methods which improve the uniformity of radiation patterning of a photoresist during reticle fabrication.
Difficulties can also occur during the formation and processing of photoresist on semiconductor wafers during formation of integrated circuitry. For instance, multiple layers of patterned photoresist can be utilized in fabrication of semiconductor circuitry on a wafer. Typically, a separate patterned layer of photoresist will be utilized for forming each layer of circuitry. It is important that each subsequent layer of photoresist be aligned exactly with the preceding layers of photoresist so that the respective layers of circuitry are appropriately aligned with one another. Occasionally, subsequent layers of photoresist do not align with preceding layers of photoresist, and such can render circuitry formed on the wafer to be inoperable. It would accordingly be desirable to develop methods which reduce a risk of misalignment of subsequent photoresist layers relative to preceding photoresist layers.
In one aspect, the invention encompasses a method of forming photoresist on a semiconductor wafer. A wafer is coated with a first layer of photoresist to define a first photoresist-coated wafer. The first photoresist-coated wafer is placed on a temperature-regulated mass and thermally equilibrated to a temperature. Subsequently, the first photoresist-coated wafer is photo-processed. After the photo-processing, the wafer is coated with a second layer of photoresist to define a second photoresist-coated wafer. The second photoresist-coated wafer is placed on the temperature-regulated mass and thermally equilibrated to the same temperature that the first photoresist-coated wafer had been equilibrated to. Subsequently, the second layer of photoresist is photo-processed.
In another aspect, the invention encompasses a reticle forming method. A layer of masking material is formed over a reticle substrate, and the reticle substrate is then placed on a temperature-regulated mass. The masking material is exposed to a patterning beam while the reticle is on the temperature-regulated mass, and the temperature-regulated mass holds the temperature of the reticle substrate about constant during such exposing.